单选题设函数f(r)当r＞0时具有二阶连续导数，令，则当x，y，z与t不全为零时=A．B．C．D．

单选题当x→0时，与1-cosx比较，可得______A．是较1-cosx高阶的无穷小量B．是较1-cosx低阶的无穷小量C．与1-cosx是同阶无穷小量，但不是等价无穷小量D．与1-cosx是等价无穷小量

单选题设D为y=x，x=0，y=1所围成区域，则A．B．C．D．

单选题曲线的渐近线条数为()

单选题{{B}}Directions:{{/B}} There are 15 questions in this part of the test. Read the passage through. Then, go back and choose one suitable word or phrase marked A, B, C or D for each blank in the passage. Mark the corresponding letter of the word or phrase you have chosen with a single bar across the square brackets on your Machine-scoring Answer Sheet. Acid rain leads to fish mortality. Many species of fish cannot survive in aquatic environments where the pH is below 5.0. If the water is too acid, the gill systems of many kinds of fish can be damaged.{{U}} {{U}} 1 {{/U}} {{/U}}, the acid alters the blood chemistry of all fish. As a result, the fish population in an acidic environment decreases{{U}} {{U}} 2 {{/U}} {{/U}}becomes extinct.Approximately 20 percent of the lakes in Scandinavia are without fish. Moreover, in Nova Scotia the{{U}} {{U}} 3 {{/U}} {{/U}}salmon industry may be threatened by the decrease of salmon in rivers and streams. The impact is also{{U}} {{U}} 4 {{/U}} {{/U}}in the waters of Ontario and Quebec, where fish populations are (25) the decline. What potential remedies exist for the acid rain{{U}} {{U}} 5 {{/U}} {{/U}}? The experts disagree. Some say new environmental laws should be{{U}} {{U}} 6 {{/U}} {{/U}}to control the emission of pollutants in the atmosphere. Some say that if we had known how serious acid rain was, we would have planned{{U}} {{U}} 7 {{/U}} {{/U}}to prevent it.{{U}} {{U}} 8 {{/U}} {{/U}}, all agree that if the consumption of fossil fuel were reduced, we would have less of a problem. Another{{U}} {{U}} 9 {{/U}} {{/U}}is that special scrubbers could be installed in smokestacks to remove a good{{U}} {{U}} 10 {{/U}} {{/U}}of the pollutants before they get into the atmosphere. Other ideas even include breeding more{{U}} {{U}} 11 {{/U}} {{/U}}fish. And research suggests that spreading lime into lakes may be effective in{{U}} {{U}} 12 {{/U}} {{/U}}acidity. In conclusion, it is clear that if we truly want to reduce the impact of acid rain, a{{U}} {{U}} 13 {{/U}} {{/U}}of remedies and international cooperation must be explored. It is a sad fact that acid rain probably could have been avoided if we{{U}} {{U}} 14 {{/U}} {{/U}}what we know now.

单选题n维向量组α1，α2，…，αs线性无关的充分条件是( )。 A．α1，α2，…，αs均不是零向量 B．α1，α2，…，αs中任意两个向量的分量不成比例 C．向量α1，α2，…，αs的个数s≤n D．某向量β可以由α1，α2，…，αs线性表示，且表示式唯一

单选题设

单选题某厂加工一批零件，甲车间加工这批零件的20%，乙车间加工剩下的25%，丙车间加工再余下的40%，还剩3600个零件没有加工，这批零件一共有{{U}} {{/U}}． A. 9000个 B. 9500 C. 9800个 D. 10000个

单选题方程所表示的曲线是()．A．圆B．椭圆C．抛物线D．双曲线

单选题m=-4或m=一3(1)直线l1:(3+m)x+4y=5，l2：mx+(3+m)y=8互相垂直(2)点A(1，0)关于直线x一y+1=0的对称点是

单选题设函数f(x)在[-1，1]上有定义，在x=0处可导，则f'(0)=0是级数收敛的A．充分条件．B．必要条件．C．充分必要条件．D．既非充分也非必要条件．

单选题A．B．0C．ln2D．-ln2

单选题若